1. Field
The invention is in the field of devices for measuring the liquid level in a liquid reservoir such as measuring the level of oil in the crankcase of an engine or the level of transmission fluid in a transmission to determine if such level is above a predetermined level.
2. State of the Art
There are many situations where it is desireable to measure the level of a liquid in a reservoir but where an absolute measurement is not required, only a determination as to whether the level of liquid in the reservoir is above a predetermined minimum level. Thus, in an automobile crankcase, it is not usually important to know the exact level of the oil in the crankcase, but only if the oil is above the level where it is necessary to add a quart of oil. The same is true of the level of transmission fluid in an automobile transmission and of most other automobile fluid levels.
U.S. Pat. Nos. 4,649,746 and 4,831,877 show devices which measure fluid level in a reservoir and when used to measure oil or transmission fluid level in an automobile, take the place of the normal dipstick. The advantage of the devices of the cited patents are that the oil level can be determined by merely depressing an easily accessible plunger and it is not necessary to actually grasp the dipstick, remove it, wipe it clean of fluid, replace it, remove it again and attempt to read the fluid level on the dipstick. The level indicators of the cited patents remove most of the chance of getting oil, grease, or other fluids on clothing during checking of fluid levels.
While the devices of the cited patents work well and provide an accurate indication of actual fluid level in the reservoir, such devices have so far been found to be difficult to manufacture at a price which is attractive tot he automotive after-market.